A 6-4 6-0 demolition of fourth seed Elina Svitolina earned the world No. 37 what she described as the biggest win of her career and a spot in the Australian Open's final four.

Her opponent later revealed she had struggled with a hip injury, but unseeded Mertens was virtually unstoppable.

In her debut at the grand slam, she'd had no expectations.

As for what has played out? She never could have imagined.

"It's amazing … not expected," she said.

"I was in the zone.

"I played a qualifier first round, so I was expected to win.

"Not always easy, but yeah, as it moved forward, first round, second round, I didn't really expect to be in the semis."

Her confidence only continues to grow.

The 22-year-old remains in touch with one-time idol and now mentor Kim Clijsters, who won the 2013 Australian Open and three US Open titles.

She was the last Belgian to make a semi-final at Melbourne Park, six years ago.

Clijsters has been offering support via text throughout the tournament, with Mertens - who trains at Clijsters' Belgium academy - sure there would have been another waiting when she finally turned on her phone in the wake of the victory.

"Don't be too stressy," had been the pre-match message.

It worked.

Australia agrees with the "quiet girl".

She has won the Hobart International two years running, with this semi-final berth a product of a gruelling six-week training block and an "atmosphere" that Mertens has grown to love.

"Of course I did preseason at home in Belgium, for six weeks," she said.